Resistance to the permeation of gases and liquid is a required characteristic of modern packaging materials. In addition these materials are required to have good mechanical properties. While polycarbonate is an excellent material for molding a variety of plastic articles including films and packaging, its barrier properties are somewhat deficient. The combination of polyvinylidene chloride--a material known for its excellent barrier properties--with polycarbonate resins has been alluded to in the literature yet no successful co-extruded structure containing these materials has been reported. U.S. Pat. No. 3,420,729 disclosed an article comprising an outer shell and an inner rigidifier component and an adhesive layer placed therebetween. Polycarbonate is mentioned among the suitable materials for the outer shell. Polyvinylidene chloride (saran) is disclosed in U.S. Pat. Nos. 3,561,629, 3,717,544, 3,908,070 and 4,107,362 to be suitable as the intermediate layer in a laminated article. In U.S. Pat. No. 3,606,958 there was disclosed a container having a wall comprising a load-carrying lamina and a second, sealing lamina. Polycarbonate is listed among the materials suitable for the load-bearing lamina while polyvinylidene chloride is disclosed among the suitable materials for the fluid barrier laminae. Also relevant in this connection is the container disclosed in U.S. Pat. No. 3,869,056. In U.S. Pat. No. 4,475,241 there is disclosed a packaging film which comprises a base sheet having a polycarbonate coating and an adhesive tie layer.
It is perhaps instructive to note that the art regards the coextruded structure of polycarbonate and polyvinylidene to be an impossibility. In a paper entitled "Materials and Components for High Temperature Barrier Packaging," L. E. Baccaro et al (1984 Polymers, Lamination and Coatings Conference, Book 2, Proceedings of the Technical Association of the Pulp and Paper Industry, pp 639) it was noted that among the drawbacks of polyvinylidene chloride is that "with the current coextrusion feedblock systems on the market, it is virtually impossible to process with PC without degradation". In fact, as late as 1987 in an article entitled "A Comparison of Barrier Plastics for Packaging; The packaging composites of EVOH and PVDC" by M. Boysen, Rheinberg, Kunststoffe 77 (1987) 5,pp. 522/525, it was clearly stated that coextrusion of PVDC and polycarbonates is not possible.